The present invention disclosed herein relates to a digital radio frequency (RF) converter and an RF converting method thereof, and more particularly, to a digital RF converter modulating a digital signal of a baseband into an analog signal of an RF band and an RF converting method thereof.
According to a typical analog-based RF transmitter, a digital analog converter (DAC) converts in-phase (I) and quadrature (Q) signals having a plurality of digital bits into I and Q analog signals, respectively. The digital signal has an original image component. This image component is generated at a multiple of a sampling frequency in the DAC and then is shown in the I and Q analog signals. Accordingly, a low pass filter (LPF) removes the image component from the I and Q analog signals.
Next, the I and Q analog signals passing through the LPF is up-converted into an RF signal after multiplied by I and Q local oscillator signals in a mixer and then is added. A spurious wave or noise, which is caused by a nonlinear characteristic of the mixer, is removed from the up-converted RF signal using an RF band pass filter (BPF). The RF signal passing through the RF BPF is amplified by an amplifier to be fit for transmitter output power specification and then is transmitted to an antenna through a duplex/switch.
An RF transmitter has a radical limitation that an analog circuit has. That is, in case of the analog circuit, since nonlinearity and matching property between devices are improper, entire performance of the RF transmitter may be deteriorated and performance decrease may occur especially due to temperature and process changes. Moreover, as a frequency bandwidth of a signal is increased, designing a semiconductor integrated circuit (IC) of the LPF becomes more complex and especially, since the minimum line width of a semiconductor device is reduced and a power voltage is lowered as recently, it is difficult to meet design specification during designing of the LPF. Furthermore, when the LPF and DAC are realized with an analog circuit, a broader circuit area is required.